It has been observed that the flu virus does not suddenly appear in the fall and winter seasons but is present all year around. Yet it is in the fall and winter that people tend to become much more susceptible to the flu virus and it is during these times of the year that people experience a marked increase in symptoms associated with the flu and the common cold. While there may be several dynamics associated with this increase in susceptibility to the flu virus and viruses connected with the common cold, it has been observed that vitamin D appears to be one of those dynamics.

Vitamin D regulates genetic expression in hundreds of tissues throughout the body. In the body, vitamin D converts to calcitriol which acts as a steroid hormone turning protein production on and off, as your body requires. Vitamin D has been shown to increase production of broad-spectrum antimicrobial peptides. Peptides are linked amino acids that perform specific functions in the body. There are 200 known antimicrobial peptides which act in the body to destroy the cell walls of bacteria, fungi, and viruses, including the influenza virus. When doing this, it has been shown there is a simultaneous prevention of the release of inflammatory cells, called chemokines and cytokines, into infected lung tissue. During the 1918 flu pandemic, it was found that inflammatory cytokines had triggered the complete destruction of the normal epithelial cells lining the respiratory tract. This is the kind of inflammatory reaction that vitamin D has been found to prevent.

To date, there have not been any completed clinical studies that measure the impact of vitamin D in helping prevent the flu virus from attacking the respiratory tract. There are, however, a number of observations that have been made that strongly suggest an inverse relationship between vitamin D levels in the body and the flu. In other words, as vitamin D increases, the incidence of flu decreases.

One such observation comes from Dr. Norris Glick, an MD who works at a state residential long and short-term treatment facility for individuals with developmental disabilities called Central Wisconsin Center. This Center is located in Madison Wisconsin and is managed by the State of Wisconsin's Department of Health Services, Division of Long Term Care. This facility is home to approximately 275 patients served by a staff of approximately 800. Serum levels of vitamin D have been monitored in virtually all patients for several years and patients have been supplemented with vitamin D.

In June, 2009, two patients developed influenza-like symptoms and were tested positive for H1N1 which is the swine flu virus. One patient was a long-term resident and the other patient was a child who was recently transferred to the Center.

Sixty of the staff members developed flu symptoms. Eight tested positive for H1N1. There were an additional 43 staff members who called in sick because of flu-like symptoms. Eleven or twelve staff members developed flu-like symptoms after working on the unit where the child was given care. Several of these staff members tested positive for H1N1. The patients at this Center have interaction with each other and the staff.

What is interesting is that only these two patients out of a total of 275 developed flu-like symptoms and one of the two was the child recently brought to the Center who came to the center with the flu. On the other hand, 103 of 800 staff members developed flu-like symptoms. It appears the spread of H1N1 was not from staff-to-patient but from patient-to-staff and between staff. The implication is that the staff personnel were susceptible to H1N1 while the patients, who have been provided vitamin D supplementation, were seemingly protected.

While this report doesn’t prove vitamin D was the variable that made the difference in this case, the fact that vitamin D is known to produce in the body protective mechanisms that protect against the flu virus provides circumstantial evidence that this was a determining factor in the patients of this facility not getting the flu. It should be noted that there are additional anecdotal observations of this nature from physicians and others regarding an apparent link between vitamin D levels and susceptibility to the flu.

Much research has been done with vitamin D in recent years demonstrating it has many more functions in the body than previously thought. One of these functions is associated with protecting the body from viral attack. It’s been recognized that many Americans are deficient in vitamin D, especially during the winter months when there is limited exposure to sunlight which activates the manufacture of vitamin D in the body. There is increasing evidence to suggest correlation between diminished vitamin D levels and susceptibility to the flu and other health problems.

We strongly recommend supplementing with vitamin D during the winter flu season in addition to implementing the necessary dietary changes to insure strong immunity. It is also recommended that you get tested for current blood levels of vitamin D. Such testing is available through Milk ‘N Honey.